I heard a rumor that in the 80's or 90's Hobie changed the fiberglass construction making the boats significantly lighter weight. Is this true? If so, what year did they change it? Also, how much more do the older boats weigh, how much did it cut the weight?
Another question, how is the aluminum pylon structurally attached to the hull itself?

The change wasn't so much in the way the fiberglass was done, but rather the way the hulls and decks were joined. They figured out a way to shave at least 20 lbs off the boats, and the class minimum weight was reduced from 340 lbs to 320 lbs.

This happend in 1984 (84 model year boats). They can be easily identified because the glue seam in the deck lip is red.

Unfortunately, these boats proved to be very fragile, causing a lot of warranty claims. Consequently, the boat weights went up in the late 80's as more reinforcing was added. Pressure from the class association and ISAF resulted in class minimum weight boats being built again in the early 90's.

Bottom line - 84 and some 85 boats are light (and fragile). Late 80's / early 90's boats are heavier (and more durable). Boats from about 94 on are light and durable. You never really know until you have your boat weighed

On your second question, the bottom of the pylon is glued into a rectangular, high density foam "shoe" that is fiberglassed to both sides of the hull. There's about a 1½" gap between the bottom of the shoe and the bottom of the boat to allow water to drain.

The change wasn't so much in the way the fiberglass was done, but rather the way the hulls and decks were joined. ...This happend in 1984 (84 model year boats). They can be easily identified because the glue seam in the deck lip is red....

Unfortunately, these boats proved to be very fragile, causing a lot of warranty claims...

I am not aware of any problems related to Hobie 16's per the above statement, but Hobie 18's were having failures related to the reduction of weight. The Hobie 18 was bullet proof until they removed some glass layup patches when lightening the weight. This appeared to be a weakness in the forward and possibly rear crossbar attachment points on these boats. This was finally made bullet proof again in the late 80's.

By the way, the reduction in weight was done due to competetive products being lighter. This was sales driven engineering.

The second statement (concerning warranty claims) was speculation on the racers' part (cooberated by several dealers at the time). The light boats were made for a only short period of time before the weights started up. I was the NAHCA secretary in the meetings where the 16 weights were a very hot topic between the class and the manufacturer.('89 Chicago, '90 Myrtle Beach and '91 San Diego). The reason behind the change is really moot at this point. The boat weights varied over time and that's that.

I bought an '84 red glue seam boat in 1983 that weighed 312 lbs. It had factory installed lead shot in the rear pylons to bring it up to 320. A rear pylon shoe came loose in the hull (about 1988). The starboard front pylon shoe split (with a loud bang) at the '93 Nationals in Wildwood. Both were repaired and the boat continued to be a highly competitive boat even after I sold it in 1997. It's still being raced, albeit only on Sundays at a small lake in Pontiac, MI.

I also owned a 1989 Nationals boat that weighed 345 lbs. It was a complete pig - the slowest 16 I've ever owned.

I now have a '98 that weighs 321 and is probably the fastest 16 I've owned. My biggest problem now is finding a minimum weight crew thats over the age of 10.